Re: [PATCH/RFC] rewrite `git_default_config()` using config-set API functions

Matthieu Moy [off-list ref] writes:

In general, most strings one manipulates are "const char *", it's
frequent to modify a pointer to a string, but rather rare to modify the
string itself.

We seem to have a disagreement.  Unlike git_config_get_value() that
lets callers peek the only cached copy, git_config_get_string()
gives its caller a new copy that the caller needs to free.  Such a
new string can and should be given as mutable, I would say.